1. Field of the Invention
The present invention relates to circuit means for converting a bipolar input to a unipolar output and, more particularly, to an active circuit that accepts an input signal of either positive or negative polarity and produces an output signal having an open circuit voltage similar in amplitude to the input signal amplitude but having a defined polarity.
2. Description of the Prior Art
The present invention is concerned generally with a circuit having a pair of input terminals responsive to an input signal and a pair of output terminals for providing an output signal, where it is desired that regardless of the polarity of the input signal applied to the input terminals, the output signal be similar in amplitude to the input signal and have a defined polarity.
It is obvious that such a circuit has a variety of applications. A primary application would be the protection of electronic components from damage due to the polarity of the power supply being reversed. For example, the inadvertent reversal of a battery in a handheld calculator or an electronic watch while the on/off switch is in the "on" position will often destroy the internal integrated circuits and other delicate electronic circuitry. Furthermore, the rapid discharge of the battery which would result may damage the battery or significantly shorten its life.
The most common circuit means for achieving the desired result is a bridge rectifier including four diodes connected between the input and output terminals. The primary drawback of a bridge rectifier is that the output voltage is always less than the input voltage. The exact amount of signal reduction is equal to two of the diodes forward blocking voltages. This is approximately 1.2 volts total for silicon diodes.
Another disadvantage of a silicon diode bridge rectifier is that it contains either individual diode chips or pairs of chips instead of a single chip containing all four diodes. Not being able to integrate all four diodes onto a single chip, due to the interaction between diodes which creates parasitic diodes, often causes increased production costs.